N-type polycrystalline SnSe is considered as a highly promising candidates for thermoelectric applications due to facile processing, machinability, and scalability. However, existing efforts do not enable a peak ZT value exceeding 2.0 in n-type polycrystalline SnSe. Here, we realized a significant ZT enhancement by leveraging the synergistic effects of divacancy defect and introducing resonance level into the conduction band. The resonance level and increased density of states resulting from tungsten boost the Seebeck coefficient. The combination of the enhanced electrical conductivity (achieved by increasing carrier concentration through WCl₆ doping and Se vacancies) and large Seebeck coefficient lead to a high power factor. Microstructural analyses reveal that the co-existence of divacancy defects (Se vacancies and Sn vacancies) and endotaxial W- and Cl-rich nanoprecipitates scatter phonons effectively, resulting in ultralow lattice conductivity. Ultimately, a record-high peak ZT of 2.2 at 773 K is achieved in n-type SnSe_0.92 + 0.03WCl₆.

Polycrystalline SnSe is considered as a highly promising candidate for thermoelectric applications due to its facile processing, machinability and scale-up applications. Here, we report an extraordinary peak ZT of 2.4 as well as a high average ZT of 0.9 for Ge and S codoped SnSe nanorods synthesized by a facile hydrothermal route. The highly preferentially oriented SnSe nanorods along [100] play a dominant role in scattering heat carrying phonons, resulting in ultralow lattice thermal conductivity (0.15 W m⁻¹ K⁻¹ at 873 K). The band alignment in the electronic structure of SnSe is promoted by Ge doping, contributing to a giant Seebeck coefficient and a largely enhanced power factor of 5.84 μW cm⁻¹ K⁻² at 873 K. An extraordinarily high peak ZT and a high average ZT are achieved within a wide temperature range for polycrystalline SnSe without involving toxic elements. Moreover, the reported material exhibits outstanding hardness and compressive strength induced by grain refinement. The high thermoelectric performance and mechanical properties of polycrystalline SnSe open realistic pathways for its widespread application in waste heat recovery and power generation.

Engineering the electronic band structures upon doping is crucial to improve the thermoelectric performance of materials. Understanding how dopants influence the electronic states near the Fermi level is thus a prerequisite to precisely tune band structures. Here, we demonstrate that the Sn-s states in SnTe contribute to the density of states at the top of the valence band. This is a consequence of the half-filled p-p σ-bond (metavalent bonding) and its resulting symmetry of the orbital phases at the valence band maximum (L point of the Brillouin zone). This insight provides a recipe for identifying superior dopants. The overlap between the dopant s- and the Te p-state is maximized, if the spatial overlap of both orbitals is maximized and their energetic difference is minimized. This simple design rule has enabled us to screen out Al as a very efficient dopant to enhance the local density of states for SnTe. In conjunction with doping Sb to tune the carrier concentration and alloying with AgBiTe₂ to promote band convergence, as well as introducing dislocations to impede phonon propagation, a record-high average ZT of 1.15 between 300 and 873 K and a large ZT of 0.36 at 300 K is achieved in Sn_0.8Al_0.08Sb_0.15Te-4%AgBiTe₂.

Thermoelectric technology exhibits significant potential for power generation and electronic cooling. In this study, we report the achievement of exceptional thermoelectric performance and high plasticity in stable Cu₂Se/SnSe composites. A novel matrix plainification strategy was employed to eliminate lattice vacancies within the Cu₂Se matrix of the Cu₂Se/SnSe composites, resulting in a marked improvement in carrier mobility and power factor. The presence of quasi-coherent interfaces induces phonon scattering, reducing lattice thermal conductivity without compromising carrier mobility. Consequently, a high figure of merit (ZT) of 3.3 was attained in the Cu₂Se/5 wt.% Sn_0.96Pb_0.01Zn_0.03Se composite. Additionally, the presence of high-density nanotwins imparts remarkable plasticity to the composite, yielding a compressive strain of 12%. The secondary phase contributes to the stability of the composite by hindering the extensive migration of Cu ions through bonding interactions. Our findings present a novel strategy for enhancing the thermoelectric performance of composite semiconductors, with potential applicability to other thermoelectric systems.

The recently discovered graphite–diamond hybrid materials (Gradia) with mixed sp2- and sp3-hybridizations have opened up a new direction in carbon allotropes research. Herein, we reported Gradia-HZ, constituted by interfaced graphite and hexagonal diamond parts in the unit cell, which demonstrates distinct electronic and mechanical properties. With the modulation of graphite width, Gradia-HZ exhibits unexpected topological nodal-line semimetal, semiconductor, and normal metal integrating with a distinctive Quasi-1D electronic transport capability based on first-principles calculations. More interestingly, pressure-induced graphite phase transformation might be an implementable and effective method to regulate the structure and physical properties of Gradia-HZ. The discovery of rich and peculiar physical properties in Gradia-HZ, e.g., high-conductivity metals, semiconductors with variable bandgap, and topological semimetals, will arouse great research interest to graphite–diamond hybrid materials, to promote their development and application in advanced devices.